The human heart relies on a series of one-way valves to help control the flow of blood through the chambers of the heart. For example, deoxygenated blood returns to the heart via the superior vena cava and the inferior vena cava, entering the right atrium. The heart muscle tissue contracts in a rhythmic, coordinated heartbeat, first with an atrial contraction which aids blood in the right atrium to pass through the tricuspid valve and into the right ventricle. Following atrial contraction, ventricular contraction occurs and the tricuspid valve closes. Ventricular contraction is stronger than atrial contraction, assisting blood flow through the pulmonic valve, out of the heart via the pulmonary artery, and to the lungs for oxygenation. Following the ventricular contraction, the pulmonic valve closes, preventing the backwards flow of blood from the pulmonary artery into the heart.
Oxygenated blood returns to the heart, via the pulmonary veins, entering the left atrium. Left atrial contraction assists blood in the left atrium to pass through the mitral valve and into the left ventricle. Following the atrial contraction, ensuing ventricular contraction causes mitral valve closure, and pushes oxygenated blood from the left ventricle through the aortic valve and into the aorta where it then circulates throughout the body. Following left ventricular contraction, the aortic valve closes, preventing the backwards flow of blood from the aorta into the heart.
Unfortunately, one or more of a person's heart valves can have or develop problems which adversely affect their function and, consequently, negatively impact the person's health. Generally, problems with heart valves can be organized into two categories: regurgitation and/or stenosis. Regurgitation occurs if a heart valve does not seal tightly, thereby allowing blood to flow back into a chamber rather than advancing through and out of the heart. This can cause the heart to work harder to remain an effective pump. Regurgitation is frequently observed when the mitral valve prolapses (extends back) into the left atrium during a ventricular contraction. Stenosis, by contrast, is when a heart valve does not fully patent due to stiff or fused leaflets, blood flow tract narrowing, or obstructive material buildup (e.g., calcium). The resultant narrowed outflow causes the heart to work harder to pump blood through it, possibly leading to heart failure.
Fortunately, advances in cardiac surgery, and in particular the evolution of reliable cardio-pulmonary bypass (CPB), have enabled open heart and less-invasive methods for heart valve replacement. During CPB, deoxygenated blood is diverted from the superior vena cava and inferior vena cava in or near the right atrium of the heart, brought outside the body to a CPB machine, reoxygenated, and returned to the body at the aorta, or other great arterial vessels, thereby bypassing the heart and making it possible to stop the heart for cardiac surgery.
Unfortunately, while such cardiac procedures have become common-place, they are not without risks. In particular, extended time on a CPB machine can increase a patient's chances of developing complications involving the inflammatory system, heart, lungs, kidneys, brain, etc. An inflammatory response can be triggered by blood coming into contact with the foreign substances of the tubing leading to the CPB machine and the components of the machine itself. These types of inflammatory responses can damage the endothelium (inner layer of cells) of blood vessels, making them more susceptible to platelet and clot adhesion, and ultimately to an increased chance of atherosclerosis and other cardiovascular complications. Additionally, aortic clamping, necessary to establish the CPB, may cause inadequate blood flow to certain organs, for example, the heart, lungs, kidneys, or brain, thereby leading to possible ischemic damage to those organs. The risks of complications due to CPB increase dramatically with the amount of time a patient is actively connected to the CPB machine. Accordingly, surgeons rely on a combination of specialized skills, knowledge, technologies, and teamwork to operate as efficiently as possible in order to minimize a patient's time on CPB.
Depending on the number of valves being replaced for a patient, a typical heart valve replacement surgery can last between two to six hours, one to two hours of which can be spent on a CPB machine. While the patient is on CPB, the surgeon must gain access to the heart valve, remove the pathologic valve tissue as necessary, and install a replacement valve at the location of the original valve. The valve installation process, typically requiring suture placement and fastening, can be very time consuming, especially when surgeons are operating through small access sites when employing less-invasive techniques to reduce surgical trauma. Furthermore, the suture placements can be in a wide range of different types of tissues. For example, sutures may need to be placed within thin tissues, such as the wall of the aorta, which can be in the neighborhood of 2 mm or less in thickness in the ascending portion, which is often cut to gain access for aortic valve repair or replacement. Once access is gained to the valves and chambers of the heart, however, the tissue to be sutured is much thicker. Currently, surgeons must either have separate suturing devices for different tissue situations or they must try to use a suturing device sized for thicker tissue on thinner tissue by not fully engaging the suturing device with the tissue. In the former case, having multiple suturing devices is very expensive, and in the latter case, it is difficult for the surgeon to partially engage the suturing device with the tissue in a minimally invasive surgical scenario where the surgeon is remotely manipulating the device through a small access incision. Therefore, there is a need for devices and methods which enable surgeons to reliably and efficiently place suture stitches at a variety of tissue depths using a single suturing device. In addition to reducing the cost of surgical procedures, such devices and methods can reduce the amount of time patients need to be attached to a CPB machine, thereby reducing the likelihood of CPB-related side effects. Faster and more reliable cardiac operations offer additional benefits, such as reduced surgical team fatigue and more efficient use of critical resources. Expediting cardiac surgery can also improve patient outcomes.